1. Field of the Invention
The present invention is related to a manufacturing method of a liquid crystal display device, particularly to a dyeing method applied to a dyed medium (a medium to be colored, also called xe2x80x9ca reception layer for inkxe2x80x9d, hereinafter) formed on a color filter substrate thereof prepared for the manufacturing process thereof, ink suitable for the dyeing method, and a dyeing step for supplying the ink to the medium using a ink-jet type printer (an ink-coating apparatus).
2. Description of the Related Art
In a liquid crystal display device having a color image display function, a light shielding film made of material having low optical transmissivity is formed on at least one of a pair of substrates which sandwich a layer formed of liquid crystal composition therebetween, openings are formed in regions of the light shielding film which correspond to pixels, and a layer exhibiting the high transmissivity to light in a given wavelength range compared to the light shielding film is formed at each opening region. The light shielding film which is provided with the openings for light transmission is called a black matrix. Layers which are provided to respective opening regions and allow light in a given range to pass therethrough are called color filters, and a substrate on which these color filters are formed (in many case, a so-called transparent substrate which is made of glass, synthetic regin or the like having the high optical transmissivity and the high electrical insulation) is called a color filter substrate. In the liquid crystal display device having the color image display function, the respective color filters mounted on the color filter substrate served for the liquid crystal display device are classified into a plurality of kinds corresponding to the ranges of wavelength which exhibit the high optical transmissivity. In general, the respective color filters exhibit the high optical transmissivity at any one of three kinds of wavelength ranges which respectively correspond to red, green and blue depending on the three principle colors of light. In other words, on the color filter substrate which is used in the general color liquid crystal display device, at least three kinds of color filters which have colors different from each other are formed.
As one of the manufacturing methods of a color filter substrate, there has been known a coloring resist method which forms a plural kinds of color filters by repeating a so-called photolithography process in which a substrate (eventually constituting a color filter substrate) is coated with a resist made of high-polymer resin material having pigment in a given color dispersed therein, the resist is subjected to an exposure using a photo mask and the resist is developed in accordance with an exposure pattern (resist partially removed from the color filter substrate). Further, as another one of manufacturing methods of a color filter substrate, there has been known a dyeing method in which dyed media (also called xe2x80x9creception layersxe2x80x9d) are formed at a plural portions of a substrate and dyeing material such as dyes or pigments of given colors are supplied to respective dyed medium so as to perform coloring.
As described above, the coloring resist method has to repeat the photolithography process for respective colors and hence, there exists a limitation with respect to the manufacturing throughput of the color filter substrates and eventually the manufacturing throughput of liquid crystal display devices for the color image display using such a method. Further, in the color resist method, the resist in which the pigment of a given color is dispersed flows into or is scattered into a pixel region which is disposed close to or adjacent to a pixel region in which the color filter using such a resist is formed (the pixel region in which the another color filter made of the resist in which pigment having color different from the given color is dispersed) so that there is a possibility that an undesirable kind of pigment for another color filter may be mixed into another color filter.
On the other hand, the dyeing method which coats the dyed media on the color filter substrate is classified into several kinds depending on the method (device) which supplies the dye (hereinafter called xe2x80x9cdye inkxe2x80x9d or simply called xe2x80x9cinkxe2x80x9d) to the dyed media. As one typical example of the ink supply method, there has been known a technique which is disclosed in Japanese Laid-open Patent Publication 209669/1999 or the like in which a piezoelectric transducer is used and ink is ejected from an ink chamber due to the deformation of the piezoelectric transducer. Further, as another typical example of the ink supply method, there has been a technique which is disclosed in Japanese Laid-open Patent Publication 202124/1999 in which an ink chamber is heated so as to swell bubbles generated in the inside of the ink whereby the ink is ejected. The ink supply devices used in these techniques are respectively described in xe2x80x9cTechnologies and Materials for Inkjet Printer, 1998.7.31xe2x80x9d (published by CMC Ltd., in Japanese), wherein the former is described in xe2x80x9cthe Eighth Chapter Piezoelectric-type Inkjet Printerxe2x80x9d (pages 101-111) and the latter is described in xe2x80x9cthe Seventh Chapter Thermal Jet Printerxe2x80x9d (pages 71-100). In this specification, for the convenience sake, the method for supplying ink to the color filter substrate using the former is called xe2x80x9cpiezoelectric methodxe2x80x9d or xe2x80x9celectromechanical conversion type inkjet methodxe2x80x9d and the method for supplying ink to the color filter substrate using the latter is called xe2x80x9cthermal jet methodxe2x80x9d. Further, the color filter substrate manufacturing method which colors the dyed media formed on the color filter substrate by ejecting droplets of ink toward the color filter substrate using a device including the former and the latter is generally called xe2x80x9cinkjet methodxe2x80x9d.
Two examples of the ink supply device adopting the piezoelectric method described on pages 190-191 of xe2x80x9cTechnologies and Materials for Inkjet Printerxe2x80x9d are schematically shown in FIG. 6A and FIG. 6B, while one example of the ink supply device adopting the thermal jet method described on pages 73-75 of the same literature is schematically shown in FIG. 6C. The ink supply device shown in FIG. 6A supplies ink (dye) INK into an ink chamber CHM through an ink supply passage SPP and also supplies the ink INK into a pressure chamber PRC through an orifice ORF which is formed in the ink chamber CHM. At a position which faces the orifice ORF of the ink chamber CHM in an opposed manner, a nozzle NOZ having an opening smaller than the orifice ORF is disposed and the ink INK which is supplied into the ink chamber CHM is ejected to the dyed media of the color filter substrate through the nozzle NOZ. However, since the opening of the nozzle NOZ is small, usually, there is no possibility that the ink INK which is supplied into the ink chamber CHM through the ink supply passage SPP is ejected or leaked from the opening of the nozzle NOZ.
On the other hand, a plate-like piezoelectric crystal element PZT is arranged at a side opposite to the ink chamber CHM of the pressure chamber PRC. The piezoelectric crystal element PZT shown in FIG. 6A is in the state that a given voltage is not applied to the piezoelectric crystal element PZT. When the given voltage is applied to the piezoelectric crystal element PZT, a central portion thereof is deflected to the left side in FIG. 6A so as to expand the volume of the pressure chamber PRC. That is, by applying the given voltage to the piezoelectric crystal element PZT, the ink flows into the expanded pressure chamber PRC. Thereafter, when the applying of the given voltage to the piezoelectric crystal element PZT is stopped, the piezoelectric crystal element PZT restores the shape shown in the drawing and the volume of the pressure chamber PRC also returns to the volume shown in the drawing and hence, the ink which flows into the pressure chamber PRC at the time of the expansion of the pressure chamber PRC returns to the ink chamber CHM through the orifice ORF thus increasing the pressure in the inside of the ink chamber CHM. As a result, a portion of the ink INK in the inside of the ink chamber CHM is ejected from the opening of the nozzle NOZ.
The structure of the ink supply device shown in FIG. 6B differs from the structure of the ink supply device shown in FIG. 6A in that, with respect to a nozzle NOZ, an ink supply passage SPP, a pressure chamber PRC and an ink chamber CHM are arranged in series and a piezoelectric crystal element PZT is formed in a cylindrical shape. However, the ink supply device shown in FIG. 6B adopts the same operational principle with the ink supply device shown in FIG. 6A. That is, by applying a given voltage to the piezoelectric crystal element PZT shown in FIG. 6B, the piezoelectric crystal element PZT is expanded in the circumferential direction so as to make the ink flow into the pressure chamber PRC. Subsequently, the applying of the given voltage to the piezoelectric crystal element PZT is stopped so that an excessive amount of ink is fed into the ink chamber CHM from the pressure chamber PRC through an orifice ORF so that the inside of the ink chamber CHM is pressurized whereby a portion of the ink INK is ejected from the nozzle NOZ. Here, with respect to the ink supply device shown in FIG. 6B, a micro valve MIV is arranged between the ink supply passage SPP and the pressure chamber PRC. This micro valve MIV functions as a check valve for preventing a counterflow of the ink inside the pressure chamber to the ink supply passage SPP due to the contraction of the volume of the pressure chamber PRC when the applying of the given voltage to the piezoelectric crystal element PZT is stopped.
As described above, in the method for supplying ink to the color filter substrate using the piezoelectric method, by applying the given voltage to the piezoelectric crystal element PZT, the piezoelectric crystal element PZT is mechanically deformed in the direction of an arrow shown in FIG. 6A or FIG. 6B so as to pressurize the ink chamber CHM whereby the ink INK is supplied to the dyed media formed on the color filter substrate.
On the other hand, in the thermal jet method, as shown in FIG. 6C, a heater element HTR is provided to an ink chamber CHM and ink in the inside of the ink chamber CHM is heated by the heater element HTR so as to generate bubbles in the inside of the ink whereby the ink INK is ejected. As shown in FIG. 6C, the pressure in the inside of an ink supply passage SPP which is coupled to the ink chamber CHM is set to an appropriate negative pressure to the ink chamber CHM. Accordingly, in the state that the ink chamber CHM is not heated by the heater element HTR, a meniscus of the ink at an opening OPN of the ink chamber CHM is formed such that the meniscus forms a concave surface toward a central portion of the opening. Accordingly, there is no possibility that the ink stored in the link chamber CHM is ejected or leaked from the opening OPN. However, when the ink chamber CHM is heated by the heater element HTR, bubbles are generated in the inside of the stored ink and the bubbles become large gradually. As the bubbles become large in this manner, the meniscus of the ink at the opening OPN of the ink chamber CHM is changed to form a convex surface toward the center of the opening. When the curvature of the meniscus which forms such a convex surface is increased and reaches a certain level, droplets of the ink INK are ejected from the opening OPN. Accordingly, in the method for supplying the ink toward the color filter substrate using the thermal jet method, there is no possibility that the ink is ejected through a nozzle having a small opening and hence, the method has an advantageous effect that the ink is not clogged in the nozzle compared to the piezoelectric method. However, on the other hand, the ink supply method which adopts the thermal jet method has a drawback that the formation of bubbles in the inside of the ink chamber CHM determines the ink supply conditions to the color filter substrate so that the proper control is difficult.
To the contrary, along with the improvement of the response characteristics of the piezoelectric crystal element, the piezoelectric method can reliably supply a given quantity of ink to the dyed media formed on the color filter substrate so long as the nozzle is not clogged. Further, irrespective of the piezoelectric method or the thermal jet method, in the inkjet method, by arranging a plurality of so-called inkjet heads shown in FIGS. 6A-6C in an array due to the refinement of the supply device, a plural kinds of inks can be simultaneously supplied to respective dyed media formed on the color filter substrate so that the manufacturing throughput of the color filter substrate can be remarkably enhanced compared with the coloring resist method.
As described above, the manufacturing method of color filters using the inkjet type ink supply device adopting the piezoelectric system is recognized as a suitable technique to enhance the productivity of the color filter substrates and liquid crystal display devices into which the color filter substrates are incorporated provided that the nozzles of the ink supply devices are not clogged. Further, the frequency of the clogging of the nozzle of the ink supply device which has been considered as only one weak point thereof can be decreased by improving the composition of the solution of the ink (dye). With the use of the recent ink composition disclosed in the above-mentioned Japanese Laid-open Patent Publication 209669/1999, not only the problem that the ink is clogged in the nozzle of the ink supply device is solved but also the flight linearity of the ink ejected from the nozzle is improved. Accordingly, it has been expected that by reliably supplying a given quantity of ink to the dyed media formed on the color filter substrate using the ink supply device adopting the piezoelectric method, the production of the color filter substrate having the dyed media which are dyed with the dye having a desired concentration can be realized.
However, in the reality, even with the above-mentioned improvement of the ink composition, there still remains a drawback that the difference is generated in the concentration of color among dyed media which are colored in given colors (corresponding to pixels or a group of pixels of the liquid crystal display device). That is, even when the physical properties of the ink (viscosity, surface tension, contact angle to the dyed media and the like) are optimized, the levels of the coloring concentrations of the dyed media with the dyes (this parameter being called xe2x80x9cdyeing performancexe2x80x9d) become non-uniform. Inventors of the present application have focused their attention on the correlation between parameters such as irregularities of the sizes of the ink liquid droplets ejected from the ink supply device, the evaporation speed of the ink liquid droplets and the like and the ink composition and have reviewed the dyeing performance of the ink (ink composition).
It is an object of the present invention to provide a method for producing a liquid crystal display device exhibiting no color irregularities by providing a process suitable for supplying ink to and coloring dyed media formed on a color filter substrate which is prepared in a manufacturing process of the liquid crystal display device using an inkjet method (particularly, the method using an ink supply device adopting the piezoelectric method) and by providing ink having the composition suitable for coloring of the dyed media.
To achieve the above-mentioned object, the present invention is directed to a manufacturing method of liquid crystal display device which includes a step for preparing a first substrate having a first main surface on which color filters are formed, a step for bonding the first substrate and a second substrate having a second main surface with a sealing material at respective peripheries of the first and second substrate being superposed one another so that the first main surface and the second main surface are spaced from and opposite to one another, and a step for injecting liquid crystal substances into a space enclosed by the first and second main surfaces and sealing material, wherein the color filters are formed by coloring dyed media provided on the first main surface with ink, and as the ink which colors the dyed media, material which includes dye coloring the dyed media, solvent having affinity for the dye, a volatility-adjusting agent lowering volatility of the ink below that of the solvent and a dyeing-promoter agent (also described as a dyeing-accelerating agent, or dyeing accelerator agent) indicating higher affinity for the dye and the dyed media than to the volatility-adjusting agent is used thus preparing the first substrate (color filter substrate).
In preparing the color filter substrate, it is desirable that the above-mentioned ink (color filter ink) includes the dye for coloring the dyed media in a range from 1 to 5 weight percent thereof, solvent which has affinity with the dye (dye being resolved) in a range from 10 to 80 weight percent thereof, a volatility-adjusting agent which lowers the volatility of the ink below the volatility of the solvent in a range from 1 to 40 weight percent thereof, and a dyeing-promoter agent exhibiting higher affinity for the dye and the dyed media than the volatility-adjusting agent in a range from 1 to 30 weight percent thereof. Here, the detail of the definitions and effects of the respective volatility-adjusting agent and the dyeing-promoter agent will be explained later in the embodiments of the present invention.
It is preferable to use a reagent which indicates a higher boiling point than that of the solvent as the volatility-adjusting agent, while it is preferable to use a reagent which indicates viscosity lower than that of the volatility-adjusting agent and higher than that of the solvent as the dyeing-promoter agent.
Further, as the above-mentioned dyeing-promoter agent, it is preferable to use a compound having at least one selected from a group consisting of ester linkage, peptide linkage and bonding structure which replaces a hydrogen atom which is linked with a nitrogen atom of peptide linkage with other functional group (peptide linkage having a nitrogen atom thereof modified) in molecules. For example, it is preferable to use pyrrolidone series, lactone series or the like which have a molecular structure including a cyclic portion formed by bonding a plurality of carbon atoms and at least one molecule other than one carbon by a single bond and forms at least one of ester linkage, peptide linkage and bonding structure which modifies a nitrogen atom thereof in the cyclic portion. To use the compound having the ester linkage or peptide linkage as the dyeing-promoter agent is particularly recommendable for the manufacturing method of the liquid crystal display device which forms the dyeing media by polymerizing the organic material on a main surface of at least one of a pair of the above-mentioned substrates through ester linkage, peptide linkage and bonding structure which replaces a hydrogen atom which is linked with a nitrogen atom of peptide linkage with other functional group. As an example of the organic polymer which is formed by such a polymerization, an acrylic resin or a protein film (a casein, gelatin or the like) can be named.
A specific example of the color filter ink suitable for carrying out the present invention contains the dye for coloring the dyed media which constitutes the color filter in a range from 1 to 5 weight percent thereof, water or hydrophilic solvent in a range from 10 to 80 weight percent thereof, and at least one selected from the group consisting of glycerin, dimethyl sulfoxide, and sodium lactate in a range from 1 to 40 weight percent thereof, and the at least other one selected from the another group consisting of N-methyl-2-pyrrolidone and xcex3-butyrolactone in a range from 1 to 30 weight percent thereof respectively. In this case, the above-mentioned dye may be any compound selected from a group consisting of azo complex, phthalochanine, and anthraquinone. Further, in manufacturing the color filter substrate on which the above-mentioned dyed media is formed using the ink, it is preferable to form the dyed media using any resin selected from a group consisting of acrylic resin, casein resin and gelatin resin.
To further specifically illustrate an example of the color filter ink according to the present invention, the color filter ink contains the dye which may be any compound selected from a group consisting of azo complex, phthalochanine, and anthraquinone in a range from 1 to 5 weight percent thereof, water in a range from 10 to 80 weight percent thereof, and at least one selected from the group consisting of glycerin, dimethyl sulfoxide, and sodium lactate in a range from 1 to 40 weight percent thereof, and the at least other one selected from the another group consisting of N-methyl-2-pyrrolidone and xcex3-butyrolactone in a range from 1 to 30 weight percent thereof respectively. In such ink, it is preferable to set the composition ratio of water to a range from 50 to 70 weight percent.
On the other hand, according to the present invention, in the preparation process (manufacturing process) of the color filter substrate including:
(1) a first step for forming a light shielding film having lower optical transmissivity than that of the first substrate over a first main surface of a substrate which is used as a color filter substrate of a liquid crystal display device, and then forming a plurality of openings in the light shielding film in such a manner that the opening are spaced from each other;
(2) a second step for forming dyed media made of resin which has higher optical transmissivity than that of the light shielding film in a plurality of respective openings formed through the light shielding film;
(3) a third step for coloring the dyed media formed in the respective openings by supplying droplets of the ink to a plurality of respective openings; and
(4) a fourth step for forming a protection film on the light shielding film so as to cover the respective dyed media in the plurality of respective openings with the protection film.
(5) liquid including dye coloring the dyed media, solvent for the dye, a first reagent having lower volatility than that of the solvent, and a second reagent having higher permeability into the resin constituting the dyed media than that of the solvent is utilized for the ink.
In the third step, the droplets of the ink are supplied to each of the plurality of openings from a nozzle comprising an ink chamber and volume of the ink chamber is varied by a piezoelectric crystal element.
The volume of the droplets of ink supplied to each of the plurality of openings is suitably set to an amount which falls in a range from 1 pico-liter to 100 pico-liter (a unit of volume which is also described as pL and 1 pL is equal to 10xe2x88x929 liter) corresponding to the size of the dyed media formed on the color filter substrate or the shape of nozzles used for the manufacturing of the color filter.
The reason that the volume of droplets of ink ejected from the nozzles covers such a wide range is that the manufacturing method of the color filter substrate according to the present invention is universally applicable to the manufacturing of various kinds of and versatile color filter substrates ranging from color filter substrates for small-sized liquid crystal display devices for portable telephones to color filter substrates for large-sized liquid crystal display devices for video walls installed at streets, stations or airports.
However, since the surface area of the ink droplets is changed corresponding to the change of volume of the droplets of ink, it is preferable to adjust the composition ratio of the first reagent for the purpose of appropriately suppressing the drying of the ink on the surface of the nozzles and dyed media corresponding to the ink supply device (for manufacturing of small-sized color filter substrates or for manufacturing of large-sized color filter substrates). For example, when the volume of the droplets of ink supplied to each of the plurality of openings amounts in a range from 2 pico-liter to 6 pico-liter, it is preferable that the composition ratio of the dye in the ink is set in a rage from 1 to 5 weight percent thereof, the composition ratio of the solvent in the ink is set in a range from 10 to 80 weight percent thereof, the composition ratio of the first reagent (the above-mentioned glycerin or an equivalent thereof) in the ink is set in a range from 5 to 20 weight percent thereof, and the composition ratio of the second reagent (N-methyl-2-pyrrolidone or an equivalent thereof) in the ink is set in a range from 1 to 30 weight percent thereof.
Further, when the volume of the droplets supplied to each of the plurality of openings amounts in a range from 20 pico-liter to 40 pico-liter, it is preferable that the composition ratio of the dye in the ink is set in a rage from 1 to 5 weight percent thereof, the composition ratio of the solvent in the ink is set in a range from 10 to 80 weight percent thereof, the composition ratio of the first reagent in the ink is set in a range from 30 to 40 weight percent thereof, and the composition ratio of the second reagent in the ink is set in a range from 1 to 30 weight percent thereof.
In the above-mentioned second step, the resin constituting the dyed media may be provided by forming a layer of a material having a property to be hardened by the irradiation of light thereto on the light shielding film, and then by hardening parts of the material layer by the irradiation of light from a second main surface of the substrate opposite to the first main surface of the substrate.
For forming the dyed media or the second reagent, it is preferable to use organic compound having at least one selected from ester linkage, peptide linkage and a bonding structure which replaces a hydrogen atom bonded to a nitrogen atom of the peptide linkage with other functional group in respective molecules.
It is recommendable to apply the above-mentioned manufacturing method of color filter substrates to, for example, the manufacturing of the small-sized passive matrix type liquid crystal display devices which are mounted on portable telephones. In this case, after completing the above-mentioned fourth step, a plurality of first electrodes in a stripe shape which are made of transparent conductive films are mounted on an upper portion of the protection film in parallel, and a first main surface of the substrate is bonded to the other substrate which has a main surface on which a plurality of second electrodes in a stripe shape made of transparent conductive films are formed with a sealing material which is coated on the periphery of at least one of the first main surface and the main surface of the other substrate after facing the first main surface and the main surface of the other substrate each other in an opposed manner such that the stripes of the first electrodes and the stripes of the second electrodes intersect each other. Thereafter, the liquid crystal compound is filled in a gap or space defined between the first main surface and the main surface of the other substrate. In such a manufacturing method of liquid crystal display devices, as the substrate which constitutes the color filter substrate, a soda lime glass having a silicon oxide film on the first main surface thereof is used. In manufacturing the color filter substrates of the small-sized passive matrix type liquid crystal display devices, it is preferable to set the volume of the ink droplets ejected from the ink supply device in a range from 2 to 4 pico-liter, for example.
These described above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings.